Section 16.1: Single-Phase Induction Motors cont.
Electrical Method(s) cont.
In single-phase induction motors, there are two windings (starting and running) in mechanical (spatial) quadrature which are energized by the motor’s (single-phase) voltage supply. During startup, their currents are put nearly in electrical quadrature by phase-shifting them nearly 90° apart so as to realize (mimic) a (pseudo) two-phase motor (which has starting torque)
After the motor has begun to rotate (as a two-phase motor), the starting winding is withdraw (e.g., via a centrifugal cutout switch) leaving the running (main) winding connected, which compels the motor to run as a single-phase (squirrel-cage) induction motor
The two schemes used to achieve electric current quadrature are: